A typical structure of a conventional back-illuminated CMOS image sensor is shown in FIG. 1. The conventional back-illuminated CMOS image sensor is shown to include a semiconductor substrate 100 having a front surface and a back surface. A plurality of pixel regions are formed in the front surface, and each pixel region includes a sensor element, such as a photodiode 102 and an isolation structure 106, and other devices (e.g., MOS devices) 104, adjacent to the pixel region. The back-illuminated CMOS image sensor also includes vias and contacts 1044 for connecting the active region and gates 1042 of the other devices to a multilayer interconnect structure 1046 having a plurality of metal interconnect layers that are formed after the formation of the vias (i.e., back end of line or BEOL). The back-illuminated CMOS image sensor also includes dielectric layer 112 disposed between the interconnect layers. The back-illuminated CMOS image sensor is configured to receive incident light from the back surface of substrate 100. Therefore, it is necessary to thin the back side of the substrate. However, the thinning process may cause damage and defects 108 to the back surface of the substrate. In order to isolate the defects and repair the damage, an ion implantation process is performed on the thinned back side of the substrate by forming a PN junction in the doped region 110. A laser annealing treatment may be performed after the ion implantation to melt the semiconductor substrate and activate the dopant to repair and isolate the defects.
However, these approaches have the following problems. If the laser intensity in the laser annealing process is insufficient, defects cannot be completely isolated and may enter sensor element 102, resulting in the problem of dark current. If the laser intensity in the laser annealing process is too strong, laser energy may enter multilayer interconnect structure 1046 through semiconductor substrate 100, and the thermal radiation generated by the molten semiconductor substrate may also enter multilayer interconnect structure 1046 and cause damage to the multilayer interconnect structure.
In view of the foregoing, there is a need for a novel CMOS image sensor device and method for manufacturing the same.